In the manufacture of semiconductor devices, ion implantation is used to dope semiconductors with impurities or dopants. Ion implantation systems (also called ion implanters) are commonly used to treat semiconductor workpieces, such as silicon wafers, with an ion beam in order to produce n or p type extrinsic material doping or to form passivation layers during fabrication of an integrated circuit. When used for doping semiconductors, the ion implanter injects a selected extrinsic ion species to produce the desired properties in the semiconducting material. Implanting ions generated from source materials such as antimony, arsenic or phosphorus results in “n type” extrinsic material wafers, whereas if “p type” extrinsic material wafers are desired, ions generated with source materials such as boron, or indium may be implanted.
Typical ion beam implanters include an ion source for generating positively charged ions from ionizable source materials. The generated ions are formed into a beam and directed along a predetermined beam path toward an end station. The ion beam implanter may include beam forming and shaping structures extending between the ion source and the end station. The beam forming and shaping structures maintain the ion beam and bound an elongated interior cavity or passageway through which the beam passes en route to the end station. When operating an ion implanter, this passageway can be evacuated to reduce the probability of ions being deflected from the predetermined beam path as a result of collisions with gas molecules.
Trajectories of charged particles of given kinetic energy in a magnetic field will differ for different masses (or charge-to-mass ratios) of these particles. Therefore, the part of an extracted ion beam that reaches a desired area of a semiconductor wafer or other target after passing through a constant magnetic field can be made pure, since ions of undesirable molecular weight will be deflected to positions away from the ion beam, whereby implantation of materials other than those desired can be avoided. The process of selectively separating ions of desired and undesired charge-to-mass ratios is known as mass analysis. Mass analyzers typically employ a mass analysis magnet creating a dipole magnetic field to deflect various ions in an ion beam via magnetic deflection in an arcuate passageway that effectively separates ions of different charge-to-mass ratios.
For some ion implantation systems, the physical size of the ion beam is smaller than a target workpiece, whereby the ion beam is scanned in one or more directions in order to adequately cover a surface of the target workpiece. Generally, an electrostatic or magnetic based scanner scans the ion beam in a fast direction and a mechanical device moves the target workpiece in a slow scan direction in order to provide sufficient coverage of the ion beam across the surface of the target workpiece.